The Conveyance Mirrors are a set of objects created by Adeptus Astrum, the leader of a small, research-oriented cabal called "Gibil Esagil" in the town of Brady's Glade, NE. (He hoped to use them to coordinate actions with another, larger cabal, although he was rebuffed. It is, of course, entirely possible that he might try to contact another cabal to assist in Gibil Esagil's research.) Consisting of two floor-length mirrors with Enochian glyphs carved around the frame, each mirror has a small panel on the right side of the frame, right about where a doorknob would go on a door. This panel is marked with a crown, and if it is flipped open, causes the mirror to immediately transform to a portal connecting to the opposite mirror if and only if the other mirror's panel is also flipped open (this is a safety precaution to help prevent unauthorized travel). Through this portal, one can travel across any distance to the opposite mirror.
(The mirrors are enchanted with a variation of the Correspondence 4 rote, Hermes Portal, although they are enchanted such that the rote is permanently in effect. This is fairly vulgar, and so the mirrors should probably be stored in a sanctum, lest Disbelief and Paradox rear their ugly heads.)
If the panels are closed, the mirrors will not function. If a mirror is placed facing a solid object, the object will block the portal, although a sufficiently strong character can certainly attempt to break the barrier to traverse the portal.
If a mirror is broken, both mirrors break and become inert, leaving behind eight pawns of Tass in the form of mirror shards.